It is well known that the forward speed of trains is restricted by the “hunting” motion, which corresponds to the lateral vibration of trains running at high speed. Therefore, trains have an upper speed limit, called the “critical speed.” Several attempts have been made in the past to increase the critical speed of trains. For example, Wang, Fu-Cheng and Liao, Min-Kai (2010) “The lateral stability of train suspension systems employing inerters,” Vehicle System Dynamics, 38:5, 619 have attempted to improve the critical speed by using “inerters” in the railway suspension systems.
An “inerter,” as disclosed for example in U.S. Pat. No. 7,316,303B, represents a mechanical two-terminal element configured to control the mechanical forces at the terminals such that they are proportional to the relative acceleration between the terminals. The inerter, together with a spring and a damper, provides a complete analogy between mechanical and electrical elements, which allows arbitrary passive mechanical impedances to be synthesized. Inerters have been increasingly used in mechanical systems such as car suspension systems to improve system performance.
A disadvantage of conventional train suspension system is that there is a tight trade-off between track wear and other important performance measures. Track wear is dangerous as it has been the cause of major train accidents and requires costly critical maintenance of the railway systems. In the United Kingdom, for example, 923 million GB pounds were spent on track renewals during 2007-2008. This procedure is not only costly but causes significant disruption to the train schedules and passenger's travel.
The present invention seeks to overcome the drawbacks of the prior art and reduce track wear.